In order to obtain high solids (pigment, etc.) coatings in nonaqueous fluid systems such as paints, enamels and the like, it is necessary to reduce the level of powerful mechanical forces in order to provide acceptable application viscosities. In other words, reducing the viscosity of mill base is an effective procedure in raising the solids content in a coating. Various additives have been developed which are aimed at achieving a low viscosity. For instance, it is well known in the art that the proper choice and amount of dispersant, dispersing resin and/or catalyst reduces the viscosity of coatings. Higher solids and lower VOC can be achieved by such modification, as well as improvements in film properties.
Pigment wetting may be influenced by the viscosity of the mill base, the spatial nature of the pigment particles and the surface treatment characteristics of the pigment. Surface treatments create more hydrophilic particles and lower interfacial energy between them. In an efficient grinding procedure, pigment particles formed have increased interfacial energy between them. Particles of very fine size will tend to reagglomerate and are more difficult to keep in a well dispersed state due to London/van der Waal's forces by which the solids are attracted to each other.
Low viscosity dispersing resins are used to achieve low viscosity and high solids coatings. For example, K-CRYL.RTM. 200-6 acrylic oligomer (75% solids), commercially available from King Industries, Inc., can dramatically reduce pigment association by improving the wetting of the pigments. End groups of the polymer are oriented away from pigment particles and are compatible with binder constituents. The improved wetting results in production of more primary pigment particles and a higher pigment-to-binder concentration. Grinding time is reduced and nonvolatile content increased by the acrylic modification. However, resins can often present problems in pigment dispersion, particularly in low molecular weight resins where pigments have a tendency to associate, leading to higher viscosity. Such association also increases with the addition of solvents.
Dispersing resins of higher molecular weight and having less functionality than dispersants must be used at higher levels than the dispersants. Because of their lower functionality and higher molecular weight, they have less adverse effect than dispersants. However, unexpected increases or decreases in viscosity can be caused by chemical/physical interactions between combinations of certain resins and pigments.
Dispersing agents are also often used in attempting to solve this problem. Dispersants are surface active agents, and therefore, affect the interfacial energies between pigment particles. Proper amounts of absorbed dispersants and wetting agents prevent the reagglomeration of particles formed in the grinding of mill base. Typical dispersants are bifunctional molecules with an ionic end and an organophilic end. In order to optimize the use of dispersants, enough must be used to provide a layer around the pigment particles, thereby preventing reassociation. However, excessive amounts of dispersants reduces their effectiveness.
Many different dispersing agents are known in the art. For example, U.S. Pat. No. 3,937,678 (Yasuda et al.) discloses a method for improving the rheological and suspension properties of a paint or other nonaqueous fluid system containing pigments or other solids by adding certain amide waxes and certain emulsifiable polyethylene waxes to the same. It is stated therein that the amide and polyethylene waxes used together provide a synergistic effect.
More recently, U.S. Pat. No. 4,647,647 (Haubennestal et al.) discloses the use of addition compounds obtained from the reaction of polyisocyanates, hydroxyl compounds, compounds having Zerewitinoff-active hydrogen and at least one basic group containing nitrogen, optionally in the presence of solvents and/or reaction catalysts as suitable dispersing agents.
Other dispersants are well-known in the art as being useful for reducing the viscosity of nonaqueous fluid systems. Such dispersants include Dislon.RTM.-type additives, commercially available from Kusumoto Chemicals, Ltd. In particular, Dislon.RTM. 1860 is an anionic salt of a long chain polyaminoamide with a high weight polyester acid, and Dislon.RTM. KS-873N is an amine salt of a polyether ester acid. These additives may be added at about 0.2-1.5% by weight of paint. Both of the aforementioned Kusumoto additives improve paint gloss and enhance and stabilize pigment dispersion, although they are preferentially used for different applications based upon their particular properties.
Other additives which have been found to be useful as dispersants include the Anti-Terra.RTM.-U type additives, commercially available from BYK-Chemie. These additives are salts of unsaturated polyamineamides and higher molecular weight acidic esters. The Anti-Terra-U additives also provide improved gloss and improve the stabilization of the dispersion.
Yet another class of additives comprising modified alkyds and commercially available from NUODEX, Inc. as NUOSPERSE.RTM., have been useful as pigment dispersing agents. When added in amounts of 2-4% based on the weight of pigment, the NUOSPERSE-type dispersants also improve product quality and improve dispersion stability.
Still another class of additives comprising calcium petroleum sulfonates are offered by the Lubrizol Corporation as pigment dispersing agents.
Dinonylnaphthalene sulfonic acids, commercially available from King Industries as HDNNS.RTM. acid, and a process for their manufacture are taught in U.S. Pat. No. 2,764,548 (King et al.). King et al. disclose the fact that these compounds and salts thereof are very effective rust and corrosion inhibitors in motor fuels and lubricating oils. Dinonylnaphthalene acids and sulfonates are also well known in the art to be effective as catalysts for organic binder resins in nonaqueous fluid compositions and in coating systems comprising the nonaqueous fluid composition. When used as such catalysts, the dinonylnaphthalene acids and sulfonates are provided in amounts of about 0.5-5 percent by weight based on the weight of total resin solids.
It has now surprisingly been discovered that certain dinonylnaphthalene sulfonic acids and sulfonates function as very efficient dispersants in high solids coatings when used in amounts about one-tenth as great as when used as catalysts as described above. Furthermore, it has been found that when used in optimal quantities, the dinonylnaphthalene sulfonic acids and sulfonates provide similar physical properties to nonaqueous fluid systems such as paints, etc., but provide surprisingly improved viscosity reduction over prior art dispersants.